214 SULPHUR BACTERIA 



cannot therefore be regarded as typical, for here a second 

 shock movement was superimposed upon the organism before 

 it had recovered from the effects of the first shock movement. 

 Buder's own explanation is probably correct. When an 

 organism passes into the dark it recoils in order to get back 

 into the light, the mechanism of the process, for Thiospir ilium, 

 being the rotation of the cilium round the hinder part of the 

 organism. It considers, as it were, the end in view, and if 

 this can be attained without a shock movement, then such a 

 movement does not take place. Buder thus regards the laws 

 of shock movements as aspects of a wider biological law, 

 operating to preserve the organism from destruction. Whilst 

 in agreement with the general view, it must be added that all 

 the details of his experiments do not lend support. Thus in 

 the experiment illustrated in Fig. 58 the second shock move- 

 ment which propelled the organism farther into the darkness 

 should, according to Buder's view, not have taken place, for 

 it was one which was injurious to the microbe. As this 

 particular movement, however, was made under abnormal 

 circumstances, its significance cannot be unduly stretched, 

 particularly as there are other determinants of movement 

 besides these shocks. Proof is still wanting, however, of the 

 withholding of a shock movement when the withholding would 

 be advantageous to the organism. It would, however, be 

 difficult to stage the conditions for such an occurrence. 

 Another detail which lacks conformity with Buder's view is 

 the fact that all the individuals did not exhibit the movement 

 when they passed from the light into the dark, a fact which 

 seems to diminish their importance as vital factors in the life 

 of the organisms. Here again it would be easy to imagine 

 the prevention of the movement by the intervention of other 

 factors. The conditions of movement are similar to the con- 

 ditions determining any other physiological function. It 

 takes place when several contributory factors are working in 

 unison. A general review of the facts leads to the conclusion 

 that shock movements are broadly of a protective nature, but 

 that as movements are conditioned by several factors, the 

 incidence of a shock does not invariably produce a protective 



